Friday, March 25, 2011

How Does Fire Behave in Zero Gravity?

Most of us don't know how fire behaves in zero gravity. Well... the movies were wrong.
Let's look at this picture.

Image: ynput.com

Trying to come up with a plausible explanation?
Allow me to enlighten you instead =)

Fire needs oxygen, and that's readily available in Earth's atmosphere. Out there in space we have meager(practically none) supply of oxygen, and so astronaut cannot start a fire in outer space. If there's an explosion out there in space, the fire would quickly die away rather than burning the whole thing into ashes.

Image: cinem7.com

In the spacecraft, on the other hand, is a totally different story. We have ample supply of oxygen in a spacecraft, but no gravity, which is why we often see videos of astronauts floating about in spacecraft. Here, fire can start but it doesn't behave the way it does on Earth.

Image: futurecamping.com

On Earth, gravity pulls the air onto the ground, and so we have plenty of air around us. When fire burns, it heats up the air around it, causing circulation of air--hot air rises whilst cool air gets pulled downward. The section of air close to the fire rises and pulls the fire with it. This circulation of air is the reason behind the characteristic shape of fire we see here on Earth.

But in a spacecraft hanging above us in the orbit, there is no gravity. So there is nothing to pull the air downwards--meaning there is no air circulation. It still burns the oxygen around it but there is no gravity to pull cool air downwards to enable any air circulation. The fire starts but it just stay there. It doesn't flicker as it does on Earth and if there is nothing to propel fresh air(in this case, oxygen) towards it, the fire would slowly die away.